1. Field of the Invention
This invention relates to a process for removing iron impurities from petroleum distillation residues or heavy oils. More specifically, the invention is directed to such a process in which petroleum heavy oils are magnetically treated to remove iron contents therefrom.
2. Prior Art
As has been commonly practiced in the art of petroleum refining, residual oils resulting from atmospheric or vacuum distillation of a crude petroleum oil are subjected to hydrogenative treatment with use of a fixed-bed catalyst under elevated temperature and pressure conditions so as to obtain a variety of petroleum products or starting feedstocks for chemical processing.
In most cases, such residual oils contain considerable proportions of particulate iron or iron compounds, typically sulfides, of the order of 0.1-100 microns which emanate during the transport of a crude oil from a shipping tanker through a storage tank and delivery pipe lines to a distillation plant, or which result from corrosion or wear of such distillation plant equipment. Such iron impurities often accumulated to the order of 10-100 wt.ppm would tend to deposit on a catalyst bed or in between individual catalyst particles, resulting in plugged up reactor or deteriorated catalyst. Plugged up reactor would often lead to objectionably increased pressure drop to a point where the plant operation has to be discontinued.
In U.S. Pat. No. 4,836,914 and Japanese Laid-Open Patent Publication No. 62-54790 there is disclosed the use of a high gradient magnetic separator equipped with ferromagnetic fillers for removing iron impurities from heavy oils far more efficiently compared to centrifugal separators. However, the magnetic separation process has a drawback in that on account of literal limitations to the amount of iron impurities that can be deposited on the ferromagnetic fillers, it would require a repeated cycle of alternate energization and deenergization of the ferromagnetic material when handling huge amounts of heavy residual oil to be treated. The more frequent the cycle, the less is the rate of removal of iron impurities.